TOOL-20 · Reference

Port number reference

Searchable table of well-known TCP and UDP ports. Search by port number, service name, or description.

PortProtoServiceDescription

What "well-known" actually means

Ports 0–1023 are IANA's well-known range, reserved for specific standard services (22 SSH, 80 HTTP, 443 HTTPS, 3389 RDP) — on most systems, binding to one of these requires elevated privileges. Ports 1024–49151 are registered (still assigned to specific services by convention, like 3306 MySQL or 5432 PostgreSQL, but not privilege-restricted), and 49152–65535 are ephemeral, used as temporary source ports for outbound connections, never assigned to a fixed service.

Why this matters for firewall rules

Knowing whether a port is TCP, UDP, or both changes what a firewall rule actually needs to allow — DNS (53) uses both, most web traffic is TCP-only, and getting this wrong is a common cause of a firewall rule that looks right but silently blocks half the expected traffic.

What's the difference between TCP and UDP for a given port?

TCP is connection-oriented and guarantees delivery order (web traffic, SSH, email); UDP is connectionless and faster but doesn't guarantee delivery (DNS queries, video streaming, VoIP). Some services, like DNS on port 53, use both for different purposes — UDP for typical queries, TCP for large responses.

Why do I need root/admin privileges to use ports below 1024?

It's a decades-old Unix convention, still enforced on Linux/macOS/BSD by default: binding to a well-known port (0–1023) requires elevated privileges specifically so an unprivileged process can't impersonate a standard service like SSH or HTTP on its expected port.

What are ephemeral ports actually used for?

They're the temporary source port your OS assigns automatically for outbound connections — when your browser connects to a web server on port 443, your side of that connection uses a random ephemeral port (typically 49152–65535) that gets released once the connection closes.

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Based on IANA well-known port assignments